The term “lead” is complicated because it means different things in different systems. In Marketo, a lead is a person or more technically, an e-mail address. Marketo actually made this change in terminology to refer to a ‘lead’ to a ‘person’ several years ago in an effort to minimize confusion. Many of the api names will still show ‘lead’ instead of Person for things like status and source.
On the other hand, in Salesforce, a lead is an individual or a company that has expressed interest in a product or service but has not yet become a customer. Sales teams typically work with these leads.
In Marketo, a lead, or person, may not be ready for sales yet as they could still be in the early stages of the customer journey and getting to know your company. The objective is to engage with these individuals and help them become qualified enough to be passed on as leads to your CRM.